The present invention relates to antenna systems, with broadband operating characteristics such as are used in PCS (1850-1990 MHz), Sirius Satellite Radio (2320-2332.5 MHz), and XM Satellite Radio (2332.5-2345 MHz). More particularly, the present invention relates to antenna systems with a dual antenna configuration for coupling through the glass of an automobile window.
So-called xe2x80x9cthrough-dielectric couplersxe2x80x9d are used extensively for the transmission of radio frequency (RF) signals through materials such as glass used e.g. as an automobile window or the windowpane of a building. When installed for coupling through a structure such as an automobile window, such couplers require no modification of the structure, i.e. e.g. no holes are required to pass radiofrequency (RF) transmission lines. Earlier prior art uses either capacitive or radiating slot-type structures to achieve the RF transmission.
In recent years, there has been an increase in demand for broadband-through-glass coupling mechanisms as a part of antenna systems used in e.g. automotive applications and in particular for dual antenna satellite/terrestrial applications such as Sirius Satellite Radio and XM Satellite Radio.
A through-glass antenna coupler is disclosed in U.S. Pat. No. 5,451,966 (Du et al). The Du et al coupler includes a through-glass mechanism that employs a dual radiating slot configuration in which similar slots are required on both sides of a piece of glass. Du et al describes the similar slots as planar cavities that xe2x80x9cact as radiating elements.xe2x80x9d For high efficiency coupling, such an arrangement requires precise alignment of the planar cavities, and also requires that the planar cavities be produced to tight tolerances.
What is needed is a through-coupler that achieves high reliability without requiring tight tolerances in its manufacture or precise alignment in its installation in a structure. Ideally, unlike the prior art as taught by Du et al, such a through-coupler would also avoid radiative coupling between elements, and so would be inherently more efficient than an arrangement based on radiating elements.
Accordingly, the present invention provides an apparatus for coupling through a dielectric medium, such as glass (for example the glass of an automobile window), a radiofrequency (RF) antenna signal at a frequency in an operating frequency band having a center frequency, the apparatus including: an outside coaxial conductor for providing the RF antenna signal, the outside coaxial conductor having an inner conductor and an outer conductor; and an outside dielectric substrate having a side on which a slotline is formed, the slotline consisting of a layer of metal deposited on one side of the dielectric substrate, a layer of metal in which a slot is formed extending in a slotline direction and extending to a depth reaching the surface of the dielectric substrate, the outside dielectric substrate disposed so that the side on which a layer of metal is deposited faces away from the dielectric medium, and further wherein the inner conductor of the outside coaxial conductor is electrically attached to the layer of metal on one side of the slot and the outer conductor of the outside coaxial conductor is electrically attached to the layer of metal on the other side of the slot.
In a further aspect of the invention, the apparatus also includes an inside dielectric substrate having a side on which a microstrip is provided, the inside dielectric disposed so that the side on which a microstrip is provided faces away from the dielectric medium. In this further aspect of the invention, the microstrip and the strip extend in mutually perpendicular directions, each extending beyond the other as measured from the center of the other by an amount approximately equal to a quarter of a wavelength of the center frequency of the operating frequency band.
In another, further aspect of the invention, the apparatus also includes an inside dielectric substrate having a side on which a second slotline is provided, the inside dielectric disposed so that the side on which the second slotline is provided faces away the dielectric medium. In this further aspect of the invention, the slot of the outside slotline and the slot of the inside slotline extend in mutually perpendicular directions and each extends beyond the other as measured from the center of the other by an amount approximately equal to a quarter of a wavelength of the center frequency of the operating frequency band.